Voltage generation circuit which is capable of executing high-speed boost operation

ABSTRACT

According to one embodiment, a voltage generation circuit includes a first boost circuit, a voltage division circuit, a first detection circuit, a capacitor and a first switch. The first boost circuit outputs a first voltage. The voltage division circuit divides the first voltage. The first detection circuit is configured to detect a first monitor voltage supplied to the first input terminal, based on a reference voltage which is supplied to a second input terminal of the first detection circuit, and to control an operation of the first boost circuit. The capacitor is connected between an output terminal of the first boost circuit and the first input terminal of the first detection circuit. The first switch cuts off a connection between the capacitor and the first detection circuit, based on an output signal of the first detection circuit, until the first voltage is output from the first boost circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2010-245285, filed Nov. 1, 2010,the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a voltage generationcircuit which is applied to a semiconductor memory device, for example,a NAND flash memory.

BACKGROUND

A NAND flash memory uses high voltages which are higher than an externalpower supply voltage at times of write and erase. These high voltagesare generated by using a charge pump circuit functioning as a boostcircuit. An output voltage of the charge pump circuit is detected by adetection circuit, and the operation of the charge pump circuit iscontrolled based on an output signal of the detection circuit.

When the charge pump circuit starts to operate, a ripple componentoccurs in the output voltage. In the case where such a ripple componentis to be suppressed, the boost operation delays.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the structure of an example of asemiconductor memory device to which embodiments are applied.

FIG. 2 is a circuit diagram showing the structure of a voltagegeneration circuit according to a first embodiment.

FIG. 3 is a waveform diagram showing an example of an input voltage of adetection circuit.

FIG. 4 is a timing chart for explaining the operation of the circuitshown in FIG. 2.

FIG. 5 is a circuit diagram showing the structure of a voltagegeneration circuit according to a second embodiment.

FIG. 6 is a timing chart for explaining the operation of the circuitshown in FIG. 5.

FIG. 7 is a circuit diagram showing the structure of a voltagegeneration circuit according to a third embodiment.

FIG. 8 is a waveform diagram showing an example of an input voltage of adetection circuit according to the third embodiment.

FIG. 9 is a timing chart for explaining the operation of the circuitshown in FIG. 7.

FIG. 10 is a circuit diagram showing the structure of a voltagegeneration circuit according to a fourth embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, a voltage generation circuitincludes a first boost circuit, a voltage division circuit, a firstdetection circuit, a capacitor and a first switch. The first boostcircuit outputs a first voltage. The voltage division circuit dividesthe first voltage. The first detection circuit has a first inputterminal connected to the voltage division circuit, the first detectioncircuit being configured to detect a first monitor voltage supplied tothe first input terminal, based on a reference voltage which is suppliedto a second input terminal of the first detection circuit, and tocontrol an operation of the first boost circuit. The capacitor isconnected between an output terminal of the first boost circuit and thefirst input terminal of the first detection circuit. The first switchcuts off a connection between the capacitor and the first detectioncircuit, based on an output signal of the first detection circuit, untilthe first voltage is output from the first boost circuit.

For example, in a voltage generation circuit which is applied to a NANDflash memory, in order to suppress a ripple component in an outputvoltage of a charge pump circuit (also referred to as “pump circuit”), acapacitor for compensating a phase is provided between an outputterminal of the pump circuit and an input terminal of a detectioncircuit. However, in the case where this capacitor is provided, theoutput voltage of the pump circuit quickly rises at the time ofactivating the pump circuit, and consequently a monitor voltage of thedetection circuit rises to a reference voltage or more due to couplingof the capacitor. As a result, the detection circuit malfunctions, andthe operation of the pump circuit is stopped. The operation and stop ofthe pump circuit are repeated, and the boost operation itself of thepump circuit delays. In the embodiment, the speed of the detectionoperation of the detection circuit is increased, and the speed of theboost operation of the pump circuit is increased.

Embodiments will now be described with reference to the accompanyingdrawings.

FIG. 1 shows the structure of a NAND flash memory functioning as asemiconductor memory device to which the embodiments are applied.

A memory cell array 1 includes a plurality of bit lines, a plurality ofword lines, and common source lines. In the memory cell array 1,electrically data rewritable memory cells, which are composed of, e.g.EEPROM cells, are arranged in a matrix. A bit line control circuit 2 forcontrolling the bit lines and a word line control circuit 6 areconnected to the memory cell array 1.

The bit line control circuit 2 executes such operations as reading outdata of memory cells in the memory cell array 1 via the bit lines,detecting the states of the memory cells in the memory cell array 1 viathe bit lines, and writing data in the memory cells by applying a writecontrol voltage to the memory cells in the memory cell array 1 via thebit lines. A column decoder 3 and a data input/output buffer 4 areconnected to the bit line control circuit 2. Data storage circuits inthe bit line control circuit 2 are selected by the column decoder 3. Thedata of the memory cell, which has been read out to the data storagecircuit, is output to the outside from a data input/output terminal 5via the data input/output buffer 4. The data input/output terminal 5 isconnected to a controller 9. The controller 9 is composed of, forexample, a microcomputer, and receives data which is output from thedata input/output terminal 5. In addition, the controller 9 outputsvarious commands CMD, addresses ADD and data DT, which control theoperation of the NAND flash memory. The write data, which has been inputfrom the controller 9 to the data input/output terminal 5, is suppliedvia the data input/output buffer 4 to the data storage circuit which hasbeen selected by the column decoder 3. The commands and address aresupplied to a control signal & voltage generation circuit (hereinafteralso referred to as “boost circuit”) 7 which generates various controlsignals and voltages.

The word line control circuit 6 is connected to the memory cell array 1.The word line control circuit 6 selects a word line in the memory cellarray 1, and applies a voltage, which is necessary for read, write orerase, to the selected word line.

The memory cell array 1, bit line control circuit 2, column decoder 3,data input/output buffer 4 and word line control circuit 6 are connectedto the control signal & voltage generation circuit 7 and are controlledby this control signal & voltage generation circuit 7. The controlsignal & voltage generation circuit 7 is connected to a control signalinput terminal 8 and is controlled by control signals ALE (address latchenable), CLE (command latch enable), WE (write enable) and RE (readenable), which are input from the controller 9 via the control signalinput terminal 8. The control signal & voltage generation circuit 7includes, for example, a charge pump circuit which functions as a boostcircuit. The control signal & voltage generation circuit 7 generates,for example, a program voltage and other high voltages, which aresupplied to the word lines and bit lines, at the time of data write, andgenerates, for example, an erase voltage, which is supplied to a well,at the time of data erase.

First Embodiment

FIG. 2 shows an example of the boost circuit 7 according to a firstembodiment. The boost circuit 7 includes a charge pump circuit 11. Thecharge pump circuit 11 is composed of, for example, a series circuit ofa plurality of diode-connected transistors, and a plurality ofcapacitors which are connected at one end to connection nodes of thediodes and are supplied at the other end with a clock signal. Thestructure of the charge pump circuit 11 is not limited to this example.The charge pump circuit 11 is supplied with, for example, a power supplyvoltage VDD, a pump enable signal PMPEN which renders the pump circuitoperable, a flag signal FLG which is supplied from a detection circuit(to be described later), and a clock signal CLK. The charge pump circuit11 boosts the power supply voltage VDD, and generates a voltage VDDHwhich is higher than the power supply voltage VDD. The voltage VDDH isoutput from an output terminal.

A voltage division circuit VD is connected between the output terminalof the charge pump circuit 11 and a ground VSS terminal. The voltagedivision circuit VD is composed of a series circuit of resistors 12 and13. A connection node between the resistors 12 and 13 is connected toone of input terminals of an operational amplifier 14 which functions asa comparator. A reference voltage VREF is supplied to the other inputterminal of the operational amplifier 14. The voltage division circuitVD and operational amplifier 14 constitute a detection circuit.

The operational amplifier 14 compares the reference voltage VREF and amonitor voltage VMON which is supplied from the voltage division circuitVD. When the monitor voltage VMON exceeds the reference voltage VREF,the operational amplifier 14 outputs, for example, a flag signal FLG ofa high level from the output terminal. This flag signal FLG is suppliedto the charge pump circuit 11 and to a set input terminal S of an RSflip-flop circuit (RSFF) 15. An inversion signal PMPENB of the pumpenable signal is supplied to a reset input terminal R of the flip-flopcircuit 15.

The flip-flop circuit 15 is set by the flag signal FLG, and theflip-flop circuit 15 outputs, for example, an enable signal EN of a highlevel from a set output terminal Q and a disable signal DIS of a lowlevel from a reset output terminal Qn. In addition, the flip-flopcircuit 15 is reset by the inversion signal PMPENB.

On the other hand, one end of a capacitor 16 is connected to the outputterminal of the charge pump circuit 11. The capacitor 16 is set to sucha capacitance and a size that a ripple component can be suppressed whenthe output voltage of the charge pump circuit 11 reaches a predeterminedvoltage. The other end of the capacitor 16 is connected to the one inputterminal of the operational amplifier 14 via, for example, an N-channelMOS transistor (also referred to simply as “transistor”) 17 whichfunctions as a switch. Specifically, the series circuit of the capacitor16 and transistor 17 is connected in parallel to the resistor 12.

Besides, an N-channel MOS transistor 18, for example, which functions asa switch, is connected between a connection node CN of the capacitor 16and transistor 17 and the ground (VSS). The gate electrode of thetransistor 17 is supplied with the enable signal EN which is output fromthe set output terminal Q of the flip-flop circuit 15, and the gateelectrode of the transistor 18 is supplied with the disable signal DISwhich is output from the reset output terminal Qn of the flip-flopcircuit 15.

In the meantime, the enable signal EN and disable signal DIS, which areoutput from the flip-flop circuit 15, have such voltages that thethreshold voltages of the transistors 17 and 18 can be ignored.

The transistors 17 and 18, which function as switches, may be replacedwith, for example, transfer gates. By using the transfer gates, thevoltage VDD, instead of a high voltage, can be used for the outputvoltage of the flip-flop circuit 15.

In the above structure, the resistors 12 and 13, which constitute thevoltage division circuit VD, should desirably have high resistancevalues, thereby to reduce the consumption of current of the chip inwhich the NAND flash memory is mounted. However, when the resistors 12and 13 having high resistance values are used, the response speed of thedetection circuit lowers and the rising of the VMON, relative to theboost voltage of VDDH, delays, and, as a result, VDDH rises to apredetermined voltage or more. Thus, as shown in FIG. 3, an overshoot Aor a ripple component B occurs in the output voltage VDDH of the chargepump circuit 11. The overshoot A or ripple component B promotes thedegradation of the transistor which is supplied with the output voltageof the charge pump circuit 11.

In order to improve the response speed of the detection circuit, thecapacitor 16 for compensating the phase is provided between the outputterminal of the charge pump circuit 11 and the output node of thevoltage division circuit VD. By the capacitor 16, it is possible toimprove the response speed of the monitor voltage VMON relative to thevariation of the output voltage VDDH of the charge pump circuit 11, andto suppress the overshoot or ripple component. However, by the provisionof the capacitor 16, as described above, the detection circuitmalfunctions immediately after the charge pump circuit 11 starts boost,and the operation and stop of the charge pump circuit 11 are repeated.Thus, as indicated by C in FIG. 3, the output voltage of the charge pumpcircuit 11 varies, and the boost operation of the charge pump circuit 11is delayed. Taking this into account, in the present embodiment, thecapacitor 16 is cut off from the detection circuit during the periodfrom the start of the boost of the charge pump circuit 11 until theboost up to a predetermined voltage.

Referring to FIG. 4, the operation of the boost circuit shown in FIG. 2is described.

To start with, when the pump enable signal PMPEN is an inactive state,the flag signal FLG, which is output from the operational amplifier 14,is at a low level, and the flop-flop circuit 15 is reset by theinversion signal PMPENB of the pump enable signal PMPEN. Accordingly,the enable signal EN is at a low level and the disable signal DIS is setat a high level. The transistor 17, to the gate electrode of which theenable signal EN is supplied, is turned off, and the transistor 18, tothe gate electrode of which the disable signal DIS is supplied, isturned on. Thus, the connection node between the capacitor 16 andtransistor 18 is set at the ground potential. In addition, the monitorvoltage VMON is determined by the division of the resistors 12 and 13.

In this state, if the pump enable signal PMPEN is activated, the chargepump circuit 11 boosts the power supply voltage VDD in accordance withthe clock signal CLK. If the monitor voltage VMON of the voltagedivision circuit VD, to which the output voltage of the charge pumpcircuit 11 is supplied, becomes higher than the reference voltage VREF,the flag voltage FLG of the high level is output from the operationalamplifier 14.

Based on the flag signal FLG, the charge pump circuit 11 stops the boostoperation. In addition, the flip-flop circuit 15 is set by the flagsignal FLG. Thus, the enable signal EN, which is output from the setoutput terminal Q, is set at the high level, and the disable signal DIS,which is output from the reset output terminal Qn, is set at the lowlevel. The transistor 17, to the gate electrode of which the enablesignal EN is supplied, is turned on, and the transistor 18, to the gateelectrode of which the disable signal DIS is supplied, is turned off.Accordingly, the other end of the capacitor 16 is connected to the oneinput terminal of the operational amplifier 14 via the transistor 17.

The ON state of the transistor 17 and the OFF state of the transistor 18are held by the enable signal EN and disable signal DIS, which areoutput from the flip-flop circuit 15. Thus, even when the output signalof the charge pump circuit 11 lowers and the flag signal FLG that isoutput from the operational amplifier 14 is set at the low level, thecapacitor 16 is connected between the output terminal of the charge pumpcircuit 11 and the one input terminal of the operational amplifier 14.The capacitor 16 prevents a ripple component from occurring in theoutput voltage of the charge-pump circuit 11.

According to the above-described first embodiment, the transistor 17 isprovided between the other end of the capacitor 16, which is connectedat one end to the outpour terminal of the charge pump circuit 11, andthe one input terminal of the operational amplifier 14. When the flagsignal FLG that is output from the operational amplifier 14 is set atthe high level and the boost by the charge pump circuit 11 is completed,the transistor 17 is turned on, thereby connecting the other end of thecapacitor 16 to the one input terminal of the operational amplifier 14.Thus, when the pump circuit is activated, it is possible to preventmalfunction of the detection circuit, which would occur if the outputvoltage of the pump circuit quickly rises and the monitor voltage of thedetection circuit rises to the reference voltage or above due tocoupling of the capacitor. Thereby, such malfunction can be preventedthat the operation and stop of the pump circuit are repeated and theboost operation itself of the pump circuit delays, and it is possible tostabilize the operation of the charge pump circuit 11 and to realize ahigh-speed boost operation.

Moreover, in the case where the boost by the charge pump circuit 11 hasbeen completed, the transistor 17 is turned on and, while the chargepump circuit 11 is being activated by the pump enable signal PMPEN, theother end of the capacitor 16 is connected to the one input terminal ofthe operational amplifier 14. It is thus possible to suppress a ripplecomponent of the output voltage, when the charge pump circuit 11performs the boost operation.

Second Embodiment

FIG. 5 shows a second embodiment. In FIG. 5, the same parts as in FIG. 2are denoted by like reference numerals, and only different parts aredescribed.

In the first embodiment, one end of the current path of the transistor18 is connected to the connection node CN and the other end thereof isgrounded. By contrast, in the second embodiment, a reference voltageVREF is supplied to the other end of the current path of the transistor18.

In this structure, as shown in FIG. 6, in the state in which the pumpenable signal PMPEN is at the low level and the charge pump circuit 11is inactive, the flag signal FLG that is output from the operationalamplifier 14 is at the low level and the flip-flop circuit 15 is resetby the inversion signal PMPENB of the pump enable signal PMPEN.Accordingly, the enable signal EN is at the low level and the disablesignal DIS is at the high level. The transistor 17, to the gateelectrode of which the enable signal EN is supplied, is turned off, andthe transistor 18, to the gate electrode of which the disable signal DISis supplied, is turned on. Thus, the reference voltage VREF is suppliedto the connection node between the capacitor 16 and the transistor 18.

Thereafter, if the pump enable signal PMPEN is set at the high level,the boost operation of the charge pump circuit 11 is started. If theoutput voltage of the charge pump circuit 11 rises and the outputvoltage VMON of the voltage division circuit VD becomes higher than thereference voltage VREF, the flag signal FLG that is output from theoperational amplifier 14 rises to the high level. Accordingly, theenable signal EN that is output from the set output terminal of theflip-flop circuit 15 is set at the high level, and the disable signalDIS that is output from the reset output terminal of the flip-flopcircuit 15 is set at the low level. Hence, the transistor 18 is turnedoff and the transistor 17 is turned on. Accordingly, the potential ofthe connection node CN between the transistor 17 and capacitor 16 variesfrom the reference voltage VREF to the monitor voltage VMON. Thepotential difference between the reference voltage VREF and the monitorvoltage VMON is less than in the case of the first embodiment. It isthus possible to prevent a ripple component from occurring in the outputvoltage of the charge pump circuit 11. Therefore, the output voltage ofthe charge pump circuit 11 can stably be maintained.

By the second embodiment, too, the same advantageous effects as in thefirst embodiment can be obtained. Furthermore, according to the secondembodiment, in the inactive state of the charge pump circuit 11, thepotential of the connection node CN of the capacitor 16 is charged up tothe reference voltage VREF. Hence, when the boost by the charge pumpcircuit 11 is completed and the other end of the capacitor 16 isconnected to the one input terminal of the operational amplifier 14, theoccurrence of noise can be prevented. Therefore, it is possible toprevent a ripple component from occurring in the output voltage of thecharge pump circuit 11 and to stably maintain the output voltage.

Third Embodiment

FIG. 7 shows a third embodiment. In FIG. 7, the same parts as in FIG. 2and FIG. 5 are denoted by like reference numerals, and only differentparts are described.

In the first and second embodiments, the response speed of thearithmetic amplifier 14 at the time of activating the charge pumpcircuit 11 is improved and malfunction is prevented. In the thirdembodiment, an overshoot at the time of activating the charge pumpcircuit 11 is also improved. For this purpose, an operational amplifier19 is further provided as a second detection circuit which detects theoutput voltage of the charge pump circuit 11 earlier than theoperational amplifier 14.

Specifically, as shown in FIG. 7, the voltage division circuit VD iscomposed of a series circuit of resistors 12-1 and 12-2 and resistor 13.A monitor voltage VMON is output from a connection node between theresistor 12-2 and resistor 13, and the monitor voltage VMON is suppliedto one input terminal of the operational amplifier 14. The flag signalFLG that is output from the output terminal of the operational amplifier14 is supplied to only the charge pump circuit 11.

On the other hand, a monitor voltage VMON2, which is output from aconnection node between the resistors 12-1 and 12-2, is supplied to oneinput terminal of the operational amplifier 19, and a reference voltageVREF is supplied to the other input terminal of the operationalamplifier 19. The operational amplifier 19 compares the monitor voltageVMON2 and reference voltage VREF, and outputs, from an output terminalthereof, a flag signal FLG2 as a second flag signal which is thecomparison result. The flag signal FLG2 is supplied to a set inputterminal S of the flip-flop circuit 15.

FIG. 8 shows the relationship between the monitor voltages VMON andVMON2. The monitor voltage VMON2 is a voltage which is lower than themonitor voltage VMON. Thus, the operational amplifier 19 outputs theflag signal FLG2 before the flag signal FLG is output from theoperational amplifier 14.

In the above-described structure, as shown in FIG. 9, in the state inwhich the pump enable signal PMPEN is at the low level and the chargepump circuit 11 is inactive, the flag signal FLG2 that is output fromthe operational amplifier 19 is at the low level and the flip-flopcircuit 15 is reset by the inversion signal PMPENB of the pump enablesignal PMPEN. Accordingly, the enable signal EN is at the low level andthe disable signal DIS is at the high level. The transistor 17, to thegate electrode of which the enable signal EN is supplied, is turned off,and the transistor 18, to the gate electrode of which the disable signalDIS is supplied, is turned on. Thus, the reference voltage VREF issupplied to the connection node between the capacitor 16 and thetransistor 18.

On the other hand, if the pump enable signal PMPEN is set at the highlevel, the boost operation of the charge pump circuit 11 is started. Ifthe output voltage of the charge pump circuit 11 rises and the outputvoltage VMON2 of the voltage division circuit VD becomes higher than thereference voltage VREF, the flag signal FLG2 that is output from theoperational amplifier 19 rises to the high level. Accordingly, theenable signal EN that is output from the set output terminal of theflip-flop circuit 15 is set at the high level, and the disable signalDIS that is output from the reset output terminal of the flip-flopcircuit 15 is set at the low level. Hence, the transistor 18 is turnedoff and the transistor 17 is turned on. Accordingly, the capacitor 16 isconnected to the one input terminal of the operational amplifier 14.

Thereafter, if the output voltage of the charge pump circuit 11 furtherrises and the output voltage VMON of the voltage division circuit VDbecomes higher than the reference voltage VREF, the flag signal FLG thatis output from the operational amplifier 14 rises to the high level.Thus, the boost operation of the charge pump circuit 11 is stopped. Inthis manner, since the capacitor 16 is connected to the one inputterminal of the operational amplifier 14 before the operation of theoperational amplifier 14 is started, an overshoot of the voltage, whichis output from the charge pump circuit 11, can be suppressed.

Accordingly to the third embodiment, the operational amplifier 19 isprovided, and when the monitor voltage VMON2, which is lower than themonitor voltage VMON of the operational amplifier 14, is detected by theoperational amplifier 19, the flag signal FLG2 is output from theoperational amplifier 19. Based on the flag signal FLG2, the capacitor16 is connected to the one input terminal of the operational amplifier14. Therefore, the response speed of the detection circuit can beimproved, and the overshoot of the voltage, which is output from thecharge pump circuit 11, can be suppressed.

Moreover, immediately after the start of the boost operation of thecharge pump circuit 11, the capacitor 16 is not connected to the oneinput terminal of the operational amplifier 14. Thus, the malfunction ofthe operational amplifier 14 can be prevented, and the high-speed boostoperation can be performed.

Besides, the same advantageous effects as in the first and secondembodiments can be obtained. Therefore, it is possible to suppress anovershoot and a ripple component at high speed, and to output a stableoutput voltage.

Fourth Embodiment

FIG. 10 shows a fourth embodiment. In FIG. 10, the same parts as in FIG.2 are denoted by like reference numerals, and only different parts aredescribed.

In a NAND flash memory, in order to transfer a high voltage, which isgenerated by using a charge pump circuit, to, e.g. a memory cell array,an N-channel MOS transistor is used. In this case, in order to preventthe voltage, which is transferred, from decreasing by a degreecorresponding to a threshold voltage, it is necessary to supply avoltage, which is higher than the voltage that is transferred by adegree corresponding to the threshold voltage of the N-channel MOStransistor, to the gate electrode of the N-channel MOS transistor. Forthis purpose, it is necessary to boost the voltage that is supplied tothe gate electrode of the transistor. In order to increase the degree offreedom of circuit arrangement and to suppress the electric currentconsumption, a small-sized charge pump circuit (23 or 24 in FIG. 10) isdisposed at the gate electrode of the N-channel MOS transistor. Thischarge pump circuit is referred to as a local pump circuit.

The local pump circuit does not include a detection circuit whichdetects an output voltage and control a pump operation. Thus, even afterthe gate voltage of the transfer transistor has been sufficientlyboosted, charge/discharge of the capacitor, which constitutes the pumpcircuit, is repeated in sync with a clock signal. Consequently, electriccurrent is consumed while the local pump circuit is being activated. Agreat number of local pump circuits are used over the entirety of thechip, and this leads to a factor which increases the currentconsumption.

Taking this into account, in the fourth embodiment, the operation of thelocal pump circuit is controlled by using the detection circuit which isprovided in the charge pump circuit 11, thereby reducing the currentconsumption.

In FIG. 10, one end of the current path of an N-channel MOS transistor21 for transfer is connected to, e.g. the output terminal of the chargepump circuit 11, and the other end of the current path of the transistor21 is connected to a word line driving circuit, which is not shown. Inaddition, one end of the current path of an N-channel MOS transistor 22for transfer is connected to, e.g. the other end of the current path ofthe transistor 21. The other end of the current path of the transistor22 is connected to, e.g. a word line.

The local pump circuit 23 is supplied with, for example, a pump enablesignal PMPEN2, a clock signal CLK2 which is supplied from an AND circuit25 (to be described later), and an output voltage VDDH of the chargepump circuit 11. In the state in which the pump enable signal PMPEN2 isactivated, the local pump circuit 23 boosts the voltage VDDH, based onthe clock signal CLK2, and generates a voltage of VDDH+Vth (Vth: thethreshold voltage of the N-channel MOS transistor) or more. The outputvoltage of the local pump circuit 23 is supplied to the gate electrodeof the transistor 21.

In addition, the local pump circuit 24 is supplied with, for example, apump enable signal PMPEN3, the clock signal CLK2, and the output voltageVDDH of the charge pump circuit 11. In the state in which the pumpenable signal PMPEN3 is activated, the local pump circuit 24 boosts thevoltage VDDH, based on the clock signal CLK2, and generates a voltage ofVDDH+Vth or more. The output voltage of the local pump circuit 24 issupplied to the gate electrode of the transistor 22.

On the other hand, the flag signal FLG, which is output from theoperational amplifier 14 that constitutes the detection circuit of thecharge pump circuit 11, is supplied to the charge pump circuit 11 andflip-flop circuit 15. In addition, an inversion signal FLGB of the flagsignal FLG, which is inverted by, e.g. an inverter circuit INV, issupplied to one input terminal of a logical circuit, for instance, anAND circuit 25. A clock signal CLK, which is supplied to the charge pumpcircuit 11, is supplied to the other input terminal of the AND circuit25. The clock signal CLK2, which is output from the AND circuit 25, issupplied to the local pump circuits 23 and 24.

In the above-described structure, if the pump enable signals PMPEN,PMPEN2 and PMPEN3 rise to the high level, the charge pump circuit 11 isactivated and starts the boost operation. At this time, since the outputvoltage VMON of the division circuit VD is lower than the referencevoltage VREF, the flag signal FLG, which is output from the operationalamplifier 14 that constitutes the detection circuit, is at the lowlevel. The clock signal CLK2 is output from the output terminal of theAND circuit 25, to which the inversion signal FLGB of this flag signalis supplied. Accordingly, the local pump circuits 23 and 24 also startthe boost operation.

In this state, if the output voltage VMON of the division circuit VDbecomes higher than the reference voltage VREF, the flag signal FLG thatis output from the operational amplifier 14 is set at the high level.Thus, the boost operation of the charge pump circuit 11 is stopped. Onthe other hand, the AND circuit 25, to which the inversion signal FLGBof the flag signal FLG is supplied, stops the sending of the clocksignal CLK2. Accordingly, the local pump circuits 23 and 24 stop theboost operation. At this time, the pump enable signals PMPEN2 and PMPEN3are kept at the high level. Thus, the boosted voltages are continuouslyoutput from the output terminals of the local pump circuits 23 and 24,and the gate voltages of the transistors 21 and 22 are maintained.

The output voltage of the local pump circuit 23, 24 decreases due to anoff-leak current of the diode-connected transistors which constitute thelocal pump circuit. However, since the output voltage of the charge pumpcircuit 11 similarly decreases, if the monitor voltage VMON that isoutput from the voltage division circuit VD becomes lower than thereference voltage VREF, the flag signal FLG that is output from theoperational amplifier 14 decreases to the low level and the charge pumpcircuit 11 resumes the boost operation. At the same time, since theclock signal CLK2 is output from the AND circuit 25, the local pumpcircuit 23, 24 resumes the boost operation. By this operation, the localpump circuits 23 and 24 are controlled.

According to the fourth embodiment, the clock signal CLK2 of the localpump circuit 23, 24 is controlled by using the flag signal FLG which isoutput from the operational amplifier 14 that functions as the detectioncircuit of the charge pump 11. Therefore, the local pump circuits 23 and24 can be controlled in sync with the operation of the charge pumpcircuit 11, and an increase in electric current consumption by the localpump circuits 23 and 24 can be prevented.

FIG. 10 shows the case in which the fourth embodiment is applied to thefirst embodiment. Alternatively, the fourth embodiment can be applied tothe second and third embodiments.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. A voltage generation circuit comprising: a first boost circuitconfigured to output a first voltage; a voltage division circuitconfigured to divide the first voltage; a first detection circuit havinga first input terminal connected to the voltage division circuit, thefirst detection circuit being configured to detect a first monitorvoltage supplied to the first input terminal, based on a referencevoltage which is supplied to a second input terminal of the firstdetection circuit, and to control an operation of the first boostcircuit; a capacitor connected between an output terminal of the firstboost circuit and the first input terminal of the first detectioncircuit; and a first switch configured to cut off a connection betweenthe capacitor and the first detection circuit, based on an output signalof the first detection circuit, until the first voltage is output fromthe first boost circuit.
 2. The circuit according to claim 1, whereinthe capacitor having a first end and a second end, and furthercomprising a second switch connected between the second end of thecapacitor and a supply node of a second voltage, the second switch beingturned on when the first switch is turned off, based on the outputsignal of the first detection circuit.
 3. The circuit according to claim2, wherein the second voltage is the reference voltage.
 4. The circuitaccording to claim 3, further comprising a flip-flop circuit connectedto an output terminal of the first detection circuit, the flip-flopcircuit being configured to be set by the output signal of the firstdetection circuit and to output driving signals of the first and secondswitches.
 5. The circuit according to claim 3, further comprising asecond detection circuit having a first input terminal connected to thedivision circuit, the second detection circuit being configured todetect a second monitor voltage which is lower than the first monitorvoltage, based on a reference voltage which is supplied to a secondinput terminal of the second detection circuit; and a flip-flop circuitbeing configured to be set by an output signal of the second detectioncircuit and to output driving signals of the first and second switches.6. The circuit according to claim 4, further comprising a third switchconnected to the output terminal of the first boost circuit; a secondboost circuit configured to output a fourth voltage which drives thethird switch, based on a clock signal; and a logical circuit configuredto stop supply of the clock signal to the second boost circuit when thefirst boost circuit is stopped, based on the output signal of the firstdetection circuit.
 7. A voltage generation circuit comprising: a firstboost circuit configured to output a first voltage; a voltage divisioncircuit configured to divide the first voltage; a first detectioncircuit having a first input terminal connected to the voltage divisioncircuit, the first detection circuit being configured to detect a firstmonitor voltage supplied to the first input terminal, based on areference voltage which is supplied to a second input terminal of thefirst detection circuit, and to control an operation of the first boostcircuit; a capacitor connected to an output terminal of the first boostcircuit; and a first switch connected between the second end portion ofthe capacitor and the first input terminal of the first detectioncircuit, the first switch being configured to disconnect the second endportion of the capacitor and the first input terminal of the firstdetection circuit, based on an output signal of the first detectioncircuit, until the first voltage is output from the first boost circuit.8. The circuit according to claim 7, wherein the capacitor having afirst end and a second end, and further comprising a second switchconnected between the second end of the capacitor and a supply node of asecond voltage, the second switch being turned on when the first switchis turned off state, based on the output signal of the first detectioncircuit.
 9. The circuit according to claim 8, wherein the second voltageis the reference voltage.
 10. The circuit according to claim 9, furthercomprising a flip-flop circuit connected to an output terminal of thefirst detection circuit, the flip-flop circuit being configured to beset by the output signal of the first detection circuit and to outputdriving signals of the first and second switches.
 11. The circuitaccording to claim 9, further comprising a second detection circuithaving a first input terminal connected to the division circuit, thesecond detection circuit being configured to detect a second monitorvoltage which is lower than the first monitor voltage, based on areference voltage which is supplied to a second input terminal of thesecond detection circuit; and a flip-flop circuit being configured to beset by an output signal of the second detection circuit and to outputdriving signals of the first and second switches.
 12. The circuitaccording to claim 10, further comprising a third switch connected tothe output terminal of the first boost circuit; a second boost circuitconfigured to output a fourth voltage which drives the third switch,based on a clock signal; and a logical circuit configured to stop supplyof the clock signal to the second boost circuit when the first boostcircuit is stopped, based on the output signal of the first detectioncircuit.